As an alternative, go during the winter off season. Today, for example. You won't need reservations anywhere, crowds will be nonexistent--as will the traffic, which nobody in their enthusiam has mentioned.
Fall is the best but winter is just fine. Unfortunately, spring crowds will build streadily towards summer. The oregon coast is every bit as nice as everyone says, and you can do a whole trip just driving up and down the coast, taking in the ocean views and the little towns.
The Oregon state parks raise the bar for all parks in oregon, public and private. You'll even find some nice private parks that get mediocre reviews because they're near a cheaper--and even nicer--state park.
Did you see that sky that Prof posted? Go!